This invention relates to sheet-fed or web-fed, rotary offset or flexographic printing presses, and more particularly, to a new and improved inking/coating apparatus for the in-line application of printing inks or protective or decorative coatings to sheets or web.
Conventional sheet-fed, rotary offset printing presses typically include one or more printing units through which individual sheets are fed and printed with wet ink. After the last printing unit, the sheets are transferred by a delivery conveyor to the delivery end of the press where the freshly printed sheets are collected and stacked. In a typical sheet-fed, rotary offset printing press such as the Heidelberg Speedmaster line of presses, the delivery conveyor includes a pair of endless gripper chains carrying gripper bars and gripper fingers which grip and pull freshly printed sheets from the last impression cylinder and convey the sheets to the sheet delivery stacker.
Since the inks used with rotary offset printing presses typically remain wet and tacky for some time after printing, special precautions must be taken to insure that the freshly printed sheets are not marked or smeared as the sheets are transferred from one printing unit to another, and while being conveyed to the sheet delivery stacker. The printed surface of the sheet dries relatively slowly and can be smeared during subsequent transfer between printing units. In order to reduce smearing and offsetting, spray powder is applied on the printed sheet.
In some printing applications, offset and smearing are prevented by applying a protective and/or decorative coating over all or a portion of the freshly printed sheets. Some coating solutions include varnish, lacquer, dye, moisturizers and ink. Such coatings are formed of a UV-curable or water-dispersed resin applied as a liquid solution or emulsion over the freshly printed sheets to protect the ink and improve the appearance of the freshly printed sheets. Such coatings are particularly desirable when decorative or protective finishes are required such as in the production of posters, record jackets, brochures, magazines, folding cartons and the like. The coating is permeable to oxygen to permit drying of the ink. In cases where a liquid coating is to be applied, the coating operation is carried out after the last color ink has been printed. In some cases, it is desirable to spot coat from the printing plate. For both operations, the coating is most desirably performed by an in-line coater.
In printing presses having flexographic printing plates, an aqueous ink is used, for example metallic (gold) ink and opaque white ink, both of which can be overprinted at the next printing unit. An advantage of flexographic printing is that no dampening unit is required. The flexographic printing plate has a raised image surface (relief). Colors are stronger when flexographic inks are used because they are not diluted by dampening solution.
1. Description of the Prior Art
Various arrangements have been made for applying the coating as an in-line printing operation by using the last printing unit of the press as the coating application unit. For example, in U.S. Pat. Nos. 4,270,483, 4,685,414 and 4,779,557, there are disclosed coating apparatus which can be moved into position to allow the blanket cylinder of the last printing unit of a press to be used to apply a coating material to the sheets. In U.S. Pat. Nos. 4,796,556 and 4,841,903 there is disclosed a coating apparatus which can be selectively moved between the blanket cylinder or the plate cylinder of the last printing unit of the press so that the last printing unit can only be used for coating purposes. However, when coating apparatus of these types are used, the last printing unit cannot be used to apply ink to the sheets, but rather can only be used for the coating operation. Thus, while coating with these types of in-line coating apparatus, the press loses the capability of printing its full range of colors since the last printing unit is converted to a coating unit.
Proposals for overcoming the problem of the loss of a printing unit when in-line coating is desired have also been made, such as that set forth in U.S. Pat. No. 4,934,305 which discloses a coating apparatus having a separately timed applicator roller positioned to apply the coating material to the freshly printed sheet while the sheet is on the last impression cylinder of the press. This is said to allow the last printing unit to print and coat simultaneously, so that no loss of a printing unit capability results. Another approach to providing a coating unit without losing the printing capabilities of the last printing unit is to provide a totally separate coating unit downstream of the last printing unit so that the coating is applied to the sheets after the last printing unit. Such an arrangement is disclosed in U.S. Pat. Nos. 4,399,767, 4,706,601 and 5,176,077.
In an effort to reduce costs and maintain flexibility in adapting the printing press to different jobs, coating apparatus has been provided that can be selectively engaged with the plate cylinder or blanket cylinder to carry out the coating operation, and disengaged so that the last printing unit can be used for offset printing when coating is not required. Examples of coaters which are selectively engagable with either the plate cylinder or the blanket cylinder are disclosed in U.S. Pat. No. 4,615,293 (Jahn), U.S. Pat. No. 5,107,790 (Sliker et al.) and U.S. Pat. No. 4,841,903 (Bird).
The coater of U.S. Pat. No. 4,615,293 includes two applicator rollers, both disposed on the dampening side of the plate cylinder and blanket cylinder for carrying out spot and blanket coating operations as desired. The coater of U.S. Pat. No. 5,107,790 is retractable along an inclined rail for extending and retracting a coater head into engagement with either the plate cylinder or the blanket cylinder. Because of its size, the rail-retractable coater can only be installed between the last printing unit of the press and the delivery stacker, and cannot be used at interstation positions. The coaters of U.S. Pat. No. 4,615,293 are located on the dampener side of the plate and blanket cylinders, thus requiring removal of the dampening unit to make room for the doctor blade head and applicator rollers. Consequently, the last printing unit of the press is converted into a coating unit, resulting in the loss of the printing capability of that printing unit.
It will be appreciated that the time required to reconfigure a press for coating or non-coating is non-productive and costly. Accordingly, there is a need for a coating apparatus which minimizes the time to clean-up from one printing run and set up and run the next job. Where consecutive jobs require the same type of coating, particularly blanket coating, it may not be necessary to clean-up the coater between jobs. However, the coating cannot be allowed to dry on the rollers. Therefore, especially when switching from blanket to spot coating or vice versa, or if there is a delay between jobs, it is necessary to wash-up the coater after each job is completed.
In addition, wash-up is necessary when switching between different coating compositions, such as aqueous and ultra violet (UV) curable coatings. Such coatings are not interchangeable, and the coaters must-be washed between applications of the different coating media. It is difficult to wash-up some coaters while the press is running. Moreover, the retractable coaters mentioned above occupy a large amount of press space and diminishes accessibility to the press. Elaborate equipment is needed for retracting the coater from the operative coating position to an out-of-the-way, inoperative position which reduces access to the printing unit.
A limitation on the use of flexographic printing plates and aqueous printing inks is that the freshly printed or coated sheets require hot air for drying. When applying an aqueous ink such as opaque white or metallic gold, it is necessary to dry the printed sheets between printing units before overprinting them.
Moreover, when utilizing lithographic printing inks, it is necessary to frequently stop the press and wash the blanket. Metallic ink. in particular xe2x80x9cpilesxe2x80x9d on the blanket and must be washed frequently.
2. Objects of the Invention
Accordingly, the principal object of the present invention is to provide improved inking/coating apparatus which is capable of selectively applying ink or a coating material to a plate on a plate cylinder or a coating material to a blanket on a blanket cylinder of a printing press.
Another object of the present invention is to provide inking/coating apparatus of the character described which is extendable into inking/coating engagement with either a plate cylinder or a blanket cylinder, and which is retractable to a non-operative position to provide clear access to the cylinders of the printing unit.
A related object of the present invention is to provide inking/coating apparatus of the character described which is capable of being used in an interstation position and does not interfere with access to the press.
Yet another object of the present invention is to provide inking/coating apparatus of the character described, which can be moved from an operative inking/coating engagement position to a non-operative, retracted position.
Still another object of the present invention is to provide inking/coating apparatus of the character described, which can be used for applying aqueous inks and coatings to a lithographic printing plate or a flexographic printing plate in a rotary offset press.
A related object of the present invention is to provide inking/coating apparatus of the character described, which is capable of applying aqueous coating at, one printing unit and drying the coating before it reaches the next printing unit where it can be overprinted with aqueous ink or lithographic ink.
Another object of the present invention is to provide inking/coating apparatus for use on a multiple color rotary offset printing press that can apply ink or coating to the plate or blanket of a printing unit from a single applicator head.
A related object of the invention is to provide inking/coating apparatus of the character described, in which no printing unit adjustment or alteration is required when the applicator head is converted from plate to blanket operation and vice versa.
The foregoing objects are achieved by a retractable, in-line inking/coating apparatus which is mounted on a printing unit tower for pivotal, Ferris wheel type movement between an operative inking/coating position and a retracted, overhead position. The inking/coating apparatus includes an applicator head which extends into and retracts out of engagement with a plate on a plate cylinder or a blanket on a blanket cylinder. The inking/coating applicator head is positioned in parallel alignment with either the plate cylinder or the blanket cylinder by a carriage assembly which includes a cantilever support arm. The support arm is pivotally coupled between the inking/coating head and the printing unit tower. This cantilevered, pivotal mounting arrangement allows the inking/coating unit to be used between two printing units, as well as installed on the last printing unit of the press.
In the preferred embodiment, the applicator head includes vertically spaced pairs of cradle members with one cradle pair being adapted for supporting a metal or ceramic coating roller in alignment with a blanket cylinder, and the other cradle pair supporting a resilient anilox coating roller in alignment with the plate cylinder, respectively, when the applicator head is in the operative position. Because of the cantilevered, pivotal support provided by the support arm, the applicator head can be lifted and lowered through an arc, similar to Ferris wheel movement, in the limited space between adjacent printing units. When fully retracted, the coater and carriage assembly are lifted to an overhead position overlying the printing unit tower, thus providing complete access to the printing unit cylinders, without causing the printing unit to lose its printing capability. The inking/coating applicator roller can be inspected, cleaned or replaced and the doctor blade assembly can be washed-up automatically while the inking/coating apparatus is in the fully retracted position.
When the inking/coating apparatus is used in combination with a flexographic printing plate and aqueous ink or aqueous coating, the water component of the aqueous ink or coating on the freshly printed sheet is evaporated by a high velocity, hot air interstation dryer and a high volume heat and moisture extractor assembly so that the freshly printed ink or coating is completely dry before the sheet is printed on the next printing unit. This quick drying flexographic printing/coating arrangement permits a base coat of ink, for example opaque white or metallic ink (gold, silver or other metallics) to be applied in the first printing unit, and then overprinted by the lithographic process on the next printing unit.
Other features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings which disclose, by way of example, the principles of the present invention.